This application claims the priority of Korean Patent Application No. 2002-84089, filed on Dec. 26, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a field emission display and a method of manufacturing the same, and more particularly, to a double gate-type field emission display.
2. Description of the Related Art
In some cases, when electrons are emitted from an electron emission source of a field emission display, an arc discharge occurs in a vacuum space between a cathode plate where the electron emission source is provided and an anode plate having a fluorescent surface, which the electrons collide with. Such an arcing phenomenon supposedly takes place due to an electron discharge phenomenon occurring when a considerable amount of gas is ionized (avalanche phenomenon) because of outgassing. Sometimes, the arcing phenomenon occurs when a chamber of a field emission array (FEA) formed on the cathode plate is being tested or when an anode voltage no smaller than 1 KV is applied to the cathode plate and the anode plate, which are integrated into one body. Since edges of a gate hole are considered as belonging to a high electric field and the arcing phenomenon is more likely to occur in a high electric field, the edges of the gate hole are most vulnerable to damage caused by the arcing phenomenon, as detected by observing the surface of the FEA with an optical microscope. The arcing phenomenon causes a short circuit to occur between an anode, to which a highest potential, i.e., a positive voltage, is applied, and a gate electrode, to which a gate voltage lower than the positive voltage is applied. As a result of the short circuit between the anode and the gate electrode, the positive voltage is applied to the gate electrode, which damages a resistive layer formed on a gate oxide layer for electrically insulating a cathode electrode from the gate electrode and the cathode electrode. As the positive voltage increases, the probability of the resistive layer being damaged continues to grow. In the case of applying a positive voltage no smaller than 1 kV, the arcing phenomenon is even more likely to occur. Accordingly, in such case, it is impossible to obtain a high brightness field emission display which can stably operate even at a high voltage by adopting a simple structure of a conventional field emission display where an anode and a cathode are separated by spacers.
In the conventional field emission display, electrons extracted from a gate electrode travel toward a fluorescent surface while increasing their speeds, and thus some of the electrons may collide with the fluorescent surface beyond a given pixel due to diffusion of electron beams. This problem can be solved by providing an additional electrode for controlling electron beams on a predetermined electron beam path, i.e., focusing electron beams on a desired location on the fluorescent surface. The additional electrode corresponds to a second gate electrode in a field emission display and is formed as a single element, unlike first gate electrodes formed as stripes. The second gate electrode also prevents an arcing phenomenon from occurring in a field emission display. In this disclosure, a double gate field emission display having the second gate electrode is disclosed.
In the field emission display taught by U.S. Pat. No. 5,710,483, a second gate electrode is formed by deposition of a metal material. In a field emission display disclosed in Korean Patent Laid Open No. 2001-0081496, a metal mesh, manufactured separately from a cathode plate and an anode plate, is bridged to the cathode plate and the anode plate via spacers provided between the anode plate and the cathode plate
As taught by U.S. Pat. No. 5,710,483, the size of the second gate electrode formed by metal deposition is dependent on the size of deposition equipment. Since the size of deposition equipment limits the size of the second gate electrode to a predetermined level or below, the patented technique is not appropriate for the manufacture of a large-sized field emission device. In order to manufacture a large-sized field emission device by taking advantage of the patented technique, metal layer deposition equipment must be newly designed and manufactured to be appropriate for the manufacture of a large-sized field emission display, which requires a considerable amount of money. In the patented technique, the thickness of the second gate electrode formed by metal deposition is limited to a maximum of 1.5 microns, which is not large enough to effectively control electron beams.
On the other hand, in the case of the field emission display taught by Korean Patent Laid Open No. 2001-0081496, a second gate electrode, i.e., a mesh grid, electrode is formed of a metal plate. Accordingly, unlike in U.S. Pat. No. 5,710,483, there is no limit in the size of the second gate electrode. Rather, the thickness of the second gate electrode can be freely selected, and thus it is possible to effectively control electron beams.
FIG. 1A is a cross-sectional view of a conventional field emission display having a mesh grid as a second gate electrode. Referring to FIG. 1, a cathode plate 10 and an anode plate 20 are separated from each other by spacers 30. Since a space between the cathode plate 10 and the anode plate 20 is vacuum, the cathode plate 10 and the anode plate 20 are firmly coupled together with the spacers 30 therebetween due to a negative pressure in the vacuum space.
A cathode electrode 12 is formed on a rear plate 11 of the cathode plate 10, and a gate insulation layer 13 is formed on the cathode electrode 12. The gate insulation layer 13 is formed having a through hole 13a, through which the cathode electrode 12 is exposed. An electron emission source 14, such as a carbon nano tube (CNT), is formed on the cathode electrode 12 exposed through the through hole 13a. A gate electrode 15 is formed on the gate insulation layer 13 to have a gate hole 15a corresponding to the through hole 13a. 
An anode electrode 22 is formed on a front plate 21 of the anode plate 20, a fluorescent material layer 23 is formed on a predetermined surface of the anode electrode 22 facing the gate hole 15a, and a black matrix 24 is formed on the rest of the surface of the anode electrode 22.
A mesh grid 40 is interposed between the cathode plate 10 and the anode plate 20 and is supported by the spacers 30 being distant from both the cathode plate 10 and the anode plate 20.
The mesh grid 40 includes fixing holes 41, which the spacers 30 pass through, and an electron beam control hole 42 corresponding to the gate hole 15a. The fixing holes 41 are filled with binders 43 used to couple the mesh grid 40 with the spacers 30.
A conventional method of coupling spacers with other elements in the conventional field emission display is as follows.
The spacers 300 are arranged at intervals of a predetermined distance on the anode plate 20 in which the fluorescent material layer 23 has not yet been sintered and then are fixed onto the anode plate 20. The spacers 30 fixed onto the anode plate 20 are put into the fixing holes 41 of the mesh grid 40, and then the fixing holes 41 are filled with the binders 43 for fixing the spacers 30.
Thereafter, the mesh grid 40 and the spacers 30 are aligned with each other, the binders 41 are hardened, and then the fluorescent material layer 23 is sintered. Thereafter, the anode plate 20 and the cathode plate 10 are aligned with each other and hermetically sealed.
According to the conventional method of manufacturing a field emission display, the mesh grid 40 may be deformed or misaligned with the anode plate 20 during hardening the binders 43 at a temperature of about 120° C. and plasticizing the fluorescent material layer 23 at a temperature of about 420° C., or due to a high temperature applied when hermetically sealing the anode plate 20 and the cathode plate 10. FIG. 2A is a photograph of a screen of a field emission display manufactured by a conventional method. As shown in FIG. 2, the screen is not regular but spotted.
The deformation and misalignment of the mesh grid 40 with the anode plate 20 deteriorates the performance or causes the field emission display to malfunction. Accordingly, a new method of manufacturing a field emission device capable of solving the problems of the prior art is necessary.